Low power inverted alterphasic stimulation in a cochlear implant
An alterphasic inverting stimulation strategy for use with a multichannel cochlear implant system consumes less power than similar strategies, yet provides better sound quality. The alterphasic inverting strategy is a strategy wherein stimulation pulses are strictly sequential, and wherein the timing and polarity of the channels is chosen such that positive and negative pulses are alternating in time in accordance with a defined pattern that staggers application of the pulses spatially across all the channels and inverts the polarity of pulses that are near each other either spatially or in time.
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The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/530,532, filed Dec. 17, 2003, which application is incorporated herein by reference.
BACKGROUND OF THE INVENTIONThe present invention relates to cochlear implants, and more particularly to a low power inverted alterphasic stimulation strategy that requires very little power to deliver good sound performance.
In U.S. Pat. No. 6,219,580, there is disclosed a multichannel cochlear prosthesis with flexible control of the stimulus waveforms. Such flexible control allows almost any stimulation waveform imaginable to be created using simple programming techniques. The U.S. Pat. No. 6,219,580 is incorporated herein by reference.
In U.S. Pat. No. 6,289,247, one technique for selecting a desired stimulation strategy from a multiplicity of stimulation strategies that may be used with a multichannel cochlear prosthesis is disclosed. The U.S. Pat. No. 6,289,247 is likewise incorporated herein by reference.
Despite the availability of stimulation prostheses and stimulation strategies of the type disclosed in the above patents, there continues to be a need to find a better stimulation strategy, i.e., a stimulation strategy that consumes less power yet delivers good sound performance.
SUMMARY OF THE INVENTIONThe present disclosure addresses the above and other needs by providing an alterphasic inverting strategy that consumes less power than similar strategies, yet provides better sound quality.
The alterphasic inverting strategy of the present disclosure belongs to the family of stimulation strategies that is made possible through the use of a multichannel cochlear prosthesis of the type disclosed in the referenced patents. The referenced patents teach that an almost limitless number of stimulation strategies may be formulated and programmed into a multichannel cochlear prosthesis, bounded only by the number of channels and the ingenuity of the programmer. Some representative stimulation strategies disclosed in the referenced patents include: a continuous interleaved sampler (CIS) speech processing strategy; a paired pulsatile sampler (PPS) speech processing strategy; a simultaneous speech processing strategy, e.g., SAS; a simultaneous pulsatile sampler (SPS) strategy (wherein biphasic pulses are applied to all channels simultaneously); a hybrid analog pulsatile (HAP-4) strategy (wherein a simultaneous analog strategy is applied on four channels. and a sequential CIS-type pulsatile strategy is applied on four channels); and a multiple pulsatile sample (MPS) strategy (wherein a quad pulsatile sampler (QPS) strategy is applied in which biphasic pulses are alternately applied to four channels simultaneously). The alterphasic inverting strategy of the present disclosure is not disclosed in the referenced patents, per se, because at the time the referenced patents were filed the alterphasic inverting strategy had not been specifically identified as a possible stimulation strategy, nor had the benefits of the alterphasic inverting strategy been recognized.
The alterphasic inverting strategy of the present disclosure is a strategy wherein stimulation pulses are strictly sequential, and wherein the timing and polarity of the channels is chosen such that positive and negative pulses are alternating in time in accordance with a defined pattern.
In accordance with one aspect of the disclosure, the alterphasic inverting strategy of the present disclosure provides surprisingly good sound performance compared with other similar strategies (such as an alterphasic non-inverting strategy).
In accordance with another aspect of the disclosure, the alterphasic inverting strategy of the present disclosure requires very little power.
It is thus a feature of the present disclosure to provide a speech processing strategy that requires very little power to deliver good sound performance.
The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:
Corresponding reference characters indicate corresponding components throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTIONThe following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.
Application of the pulses of electrical stimuli through the electrode contacts E1 through E16 may be performed using monopolar stimulation, bipolar stimulation, or multipolar stimulation. In monopolar stimulation, the pulses of electrical stimuli are applied between one of the electrode contacts and the reference, or indifferent, electrode contact E0. In bipolar stimulation, the pulses of electrical stimuli are applied between two of the electrode contacts, with one electrode contact functioning as the anode at any instant of time and the other functioning as the cathode at the same instant of time. In multipolar stimulation, the pulses of electrical stimuli are applied between a multiplicity (three of more) of the electrode contacts, with at least one electrode contact functioning as the anode at any instant of time, and with at least one other electrode contact functioning as the cathode at the same instant of time. A preferred technique for application of the electrical stimuli to selected ones of the electrode contacts is to use current sources associated with each electrode contact that are configured to “source” or “sink” a programmed amount of current, as described in U.S. Pat. No. 6,181,969, incorporated herein by reference.
For purposes of the Inverted Alterphasic Stimulation technique of the present disclosure, as explained more fully below, the pulses of electrical stimuli are applied monopolarly and sequentially to just one electrode at any instant of time. Such sequential stimulation offers the advantage of lower power consumption as it is carried out than do other forms of stimulation, such as stimulation strategies where pulses of electrical stimuli are applied to more than one electrode at the same instant of time.
That which is shown is
As seen in
Another way to describe the alterphasic non-inverting strategy shown in
As can be seen from
Next, with reference to
-
- E1(−), E8(+), E3(+), E10(−), E5(−), E12(+), E7(+), E14(−), E9(−), E16(+), E2(−), E11(+), E4(+), E13(−), E6(−), E15(+), . . . ;
where the polarity symbol in parenthesis indicates the polarity of the first pulse of the alterphasic pulse applied to that channel, and where a time gap of T1 seconds is inserted between the two pulses of the alterphasic pulse, as shown inFIG. 6A .
- E1(−), E8(+), E3(+), E10(−), E5(−), E12(+), E7(+), E14(−), E9(−), E16(+), E2(−), E11(+), E4(+), E13(−), E6(−), E15(+), . . . ;
Advantageously, when using the alterphasic inverting strategy as shown in
Note that the sequence of channel stimulation indicated above and in
-
- E1(−), E8(+), E3(+), E10(−), E5(−), E12(+), E7(+), E14(−), E9 (−), E16(+), E2(−), E11(+), E4(+), E13(−), E6(−), E15(+), . . . ;
where the polarity symbol in parenthesis indicates the polarity of the first pulse of the alterphasic pulse applied to that channel, and where a time gap of T1 seconds is inserted between the two pulses of the alterphasic pulse, as shown inFIG. 6A . However, this sequence of stimulation is only exemplary. Any stimulation strategy could be used where the dual goals of inverting the polarity of the pulses and staggering the pulses so as to maximize the separation distance between adjacent-in-time pulses are achieved. InFIG. 6A , for example, it is seen that the first monophasic pulse 50 is a negative pulse applied through electrode contact E1, and the next-in-time pulse that is applied is a positive monophasic pulse 51 applied through electrode contact E8, a contact that is physically separated from contact E1 by a large distance. The next-in-time pulse that is applied after the positive pulse 51 is applied through contact E8 is another positive pulse 52 that is applied through electrode contact E3. The next-in-time pulse is negative pulse 53 applied through contact E10. This pulse 52 is quite close spatially, as well as in time, to the negative pulse 50 that was applied through contact E1, hence pulse 52 is selected to be of a polarity that is opposite from that of the pulse 50 applied through contact E1. In contrast, the pulse 52 is spatially separated from the more recent-in-time pulse 51 that was applied through electrode contact E8; thus pulse 52 is of the same polarity as pulse 51 applied through electrode contact E8.
- E1(−), E8(+), E3(+), E10(−), E5(−), E12(+), E7(+), E14(−), E9 (−), E16(+), E2(−), E11(+), E4(+), E13(−), E6(−), E15(+), . . . ;
Thus, as a stimulation sequence is selected for providing stimulation pulses in accordance with the alterphasic inverting stimulation strategy of the present disclosure, the following criteria should be considered: (a) alterphasic pulses are applied to each channel that is to be used, but the monophasic pulses that make up the alterphasic pulse are separated by a time gap T1 (
A significant advantage realized through use of the alterphasic inverting stimulation strategy of the present disclosure is a reduction in power associated with operation of the cochlear implant system. Such reduction in power results from the sequential nature of the pulses that are applied, and from the decreased M-levels which result from the inverting nature of such pulses which prevents any large low frequency pulses to be present. The inverting strategy also appears to significantly improve the ability of the user to perceive sound, as well as to improve the ability of the user to discern quality of sound.
As an approximate power consumption metric, it may be assumed that the consumed power is roughly proportional to the average M-level squared times the duty cycle, or
Power∝(Average M level)2 ×duty cycle.
This quadratic relation results because the supply voltage can be proportionally lowered if the peak current is decreased. The duty cycle is the absolute value of the current sources averaged over all phases. Since all three strategies, biphasic (
To test the present disclosure, two subjects (patients) were fitted with a subset of the following strategies: (1) alternating non-inverting strategy at 20 μs pulse width and 40 μs phase width; and (2) alternating inverting strategy at 20 μs pulse width and 40 μs phase width. These fittings were compared to the setting for the subjects' baseline fitting program obtained using a conventional fitting approach (e..g, Soundwave at 20 μs). Only M-levels were determined, and T-levels were kept at zero. The obtained M-levels were also compared with pure tones (MCL) and speech (SPCH). The resulting M-level curves obtained from the two subjects are shown in
Table 1 provides some relevant comparisons obtained from subject “MW” and subject “EP” based on the mean M-level parameters
Row 1 of Table 1 shows a surprising result for the alterphasic non-inverting strategy (ALT). When fitting with pure tones, the M levels for inverting and non-inverting strategies lie very close together. Only a single channel is activated and therefore the neural responses are identical, independent of the polarity of the first phase. However, when playing speech, the M-level needs to be decreased for subject MW from 152 μs to 120 μs for the non-inverting strategy, whereas for the inverting case, the M-levels can be increased beyond the comfortable level. This is a clear indication that the nerve now reacts to the composed broad pulse. For subject EP the difference is less pronounced.
Row 2 of Table 1 compares the levels between 40 μs and 20 us. The increase in stimulation current is substantially less than the expected factor of 2. This suggests that the nerve can react on the positive and negative pulse partially independently.
Finally, row 3 of Table 1 indicates that the ALTINV strategy results in a 20% decrease of the M-levels. Thus, it appears that its quasi-biphasic nature is still more efficient than an instantaneous biphasic pulse with 100% instantaneous charge reversal.
As seen from the above description, the present disclosure may be characterized as a method for sequentially stimulating the cochlea of a subject. Such method comprises the following steps:
(1) inserting an electrode array into the cochlea, wherein the electrode array has a multiplicity of spaced-apart electrode contacts on it that, when the electrode array is fully inserted into the cochlea, are positioned spatially along the length of the cochlea;
(2) stimulating a first electrode contact on the electrode array with a monophasic pulse having a first polarity;
(3) stimulating a second electrode contact on the electrode array immediately following (or after a short delay from) stimulation of the first electrode contact with a monophasic pulse having a second polarity, wherein the second polarity (a) is the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially near the first electrode contact, and (b) the same polarity or the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially far from the first electrode contact;
(4) stimulating a third electrode contact on the electrode array immediately following (or after a short delay from) stimulation of the second electrode contact with a monophasic pulse having a third polarity, wherein the third polarity (a) is the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially near the second electrode contact, and (b) is the same polarity or the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially far from the second electrode contact;
(5) continuing to stimulate electrode contacts on the electrode array following the above pattern until a desired number of electrode contacts have been stimulated;
(6) repeating the above stimulation pattern for all of the electrode contacts on the electrode array stimulated by a monophasic pulse of one polarity by stimulating that electrode contact with a monophasic pulse of an opposite polarity, whereby a selected number of the electrode contacts on the electrode array are stimulated in accordance with an alterphasic inverting stimulation strategy; and
(7) modulating the alterphasic inverting stimulation with sound information.
In the description of the above method, the terms “spatially far” and “spatially near” are used. These are terms that are meant to be relative with respect to both the time at which a given pulse is applied to a specified electrode contact with respect to the time when other pulses are applied to other specified electrode contacts, and with respect to the physical distance the electrode contacts are separated on the electrode array. For example, with respect to
In contrast, the positive monophasic pulse 51 is considered to be “spatially far” from the negative monophasic pulse 50 because electrode contact E8—the electrode contact on which the pulse 51 is applied—is far from electrode contact E1—the electrode contact on which the pulse 50 is applied—because there are six electrode contacts that separate electrode contact E1 from electrode contact E8. Electrode contact E8 is considered spatially far from electrode contact E1 even though the pulse 51 is applied to electrode contact E8 immediately after the pulse 50 is applied to electrode contact E1; that is, even though pulse 51 is applied close in time to the application of pulse 50.
It should be noted, however, that physical proximity of two electrode contacts does not assure that the pulses applied to those contacts will be considered as “spatially near” each other. For example, in
Once an alterphasic inverting stimulation pattern has been generated using the above-described method, or an equivalent method, such pattern is modulated in an appropriate manner with sound information. Such sound information may be sensed using, e.g., an external microphone, and the sound signals generated by the microphone may then be processed so as to amplitude modulate the alterphasic inverting pulses that are applied sequentially to the electrodes of the electrode array. Because the cochlea is arranged tonotopically, e.g., where neurons near the base of the cochlea respond to high frequency sound signals, and where the neurons closer to the apex of the cochlea respond to lower frequency signals, one form of modulation that may be used with the present disclosure separates the incoming sound signals into frequency bands. Once thus separated, the signal strength in each frequency band is used to modulate the intensity (amplitude) of the stimuli that are applied to respective electrode contacts corresponding to the frequency band.
While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.
Claims
1. A method for sequentially stimulating the cochlea of a subject comprising:
- inserting an electrode array into the cochlea, the electrode array having a multiplicity of spaced-apart electrode contacts that are positioned spatially along the length of the cochlea;
- stimulating a first electrode contact on the electrode array with a monophasic pulse having a first polarity;
- stimulating a second electrode contact on the electrode array following stimulation of the first electrode contact with a monophasic pulse having a second polarity, wherein the second polarity is the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially near the first electrode contact, and wherein the second polarity is the same polarity or the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially far from the first electrode contact;
- stimulating a third electrode contact on the electrode array following stimulation of the second electrode contact with a monophasic pulse having a third polarity, wherein the third polarity is the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially near the second electrode contact, and wherein the third polarity is the same polarity or the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially far from the second electrode contact;
- continuing to stimulate electrode contacts on the electrode array following the above pattern until a desired number of electrode contacts have been stimulated;
- repeating the above stimulation pattern for all of the electrode contacts on the electrode array that are stimulated by a first monophasic pulse of one polarity by stimulating that electrode contact with a second monophasic pulse of an opposite polarity, whereby a selected number of the electrode contacts on the electrode array are stimulated sequentially in accordance with an alterphasic inverting stimulation strategy; and
- modulating the alterphasic inverting stimulation with sound information.
2. The method of claim 1 wherein the electrode array has sixteen electrode contacts, designated as E1, E2,... E16, with electrode contact E1 being the most distal electrode contact, and electrode contact E16 being the most proximal electrode contact, and wherein the sequence of applying monophasic pulses to the sixteen electrode contacts, and the polarity of the first monophasic pulses of the alterphasic pulse comprises: wherein the polarity symbol in parenthesis after each electrode contact indicates the polarity of the first pulse of the alterphasic pulse applied to that electrode contact, and wherein a time gap of T1 seconds is inserted between the two monophasic pulses of the alterphasic pulse.
- E1(−), E8(+), E3(+), E10(−), E5(−), E12(+), E7(+), E14(−), E9 (−), E16(+), E2(−), E11(+), E4(+), E13(−), E6(−), E15(+),...;
3. The method of claim 2 wherein the time gap of T1 seconds is 1 to 100 μs.
4. The method of claim 1 wherein the alterphasic inverting stimulation strategy reduces power associated with operation of a cochlear implant system.
5. The method of claim 1 wherein the alterphasic inverting stimulation strategy improves the ability of a user to perceive sound, as well as to improve the ability of the user to discern quality of sound.
6. In a multichannel cochlear stimulation system having an electrode array insertable into a human cochlea, and wherein the electrode array has a multiplicity of spaced-apart electrode contacts positioned at or near its distal end, a low power stimulation strategy for use within the cochlear stimulation system comprising:
- means for applying an alterphasic inverting stimulation strategy to at least a multiplicity of the multiplicity of electrode contacts on the electrode array, said alterphasic inverting stimulation comprises a multiplicity of cycles on a multiplicity of channels, wherein at least one cycle of the multiplicity of cycles includes alterphasic inverting monophasic pulses occurring within the multiplicity of channels; and
- means for modulating the stimulation pulses provided by the alterphasic inverting stimulation strategy with sound information.
7. In a multichannel cochlear stimulation system having an electrode array insertable into a human cochlea, and wherein the electrode array has a multiplicity of spaced-apart electrode contacts positioned at or near its distal end, a low power stimulation strategy for use within the cochlear stimulation system comprising:
- means for applying an alterphasic inverting stimulation strategy to at least a multiplicity of the multiplicity of electrode contacts on the electrode array; and
- means for modulating the stimulation pulses provided by the alterphasic inverting stimulation strategy with sound information;
- wherein the means for applying an alterphasic inverting stimulation strategy comprises: means for stimulating a first electrode contact on the electrode array with a monophasic pulse having a first polarity; means for stimulating a second electrode contact on the electrode array following stimulation of the first electrode contact with a monophasic pulse having a second polarity, wherein the second polarity is the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially near the first electrode contact, and wherein the second polarity is the same polarity or the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially far from the first electrode contact; means for stimulating a third electrode contact on the electrode array following stimulation of the second electrode contact with a monophasic pulse having a third polarity, wherein the third polarity is the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially near the second electrode contact, and wherein the third polarity is the same polarity or the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially far from the second electrode contact; means for continuing to stimulate electrode contacts on the electrode array following the above pattern until a desired number of electrode contacts have been stimulated; and means for repeating the above stimulation pattern for all of the electrode contacts on the electrode array that are stimulated by a first monophasic pulse of one polarity by stimulating that electrode contact with a second monophasic pulse of an opposite polarity, whereby a selected number of the electrode contacts on the electrode array are stimulated sequentially in accordance with the alterphasic inverting stimulation strategy.
8. The alterphasic inverting stimulation strategy of claim 7 further including means for inserting a time gap of T1 seconds between two monophasic pulses of the alterphasic pulse, wherein T1 ranges from 1 to 100 μs.
9. A method of providing a low power stimulation strategy for use within a cochlear stimulation system, said stimulation system including an electrode array insertable into a human cochlea, wherein the electrode array has a multiplicity of spaced-apart electrode contacts positioned at or near its distal end, the method comprising:
- applying an alterphasic inverting stimulation to at least a multiplicity of the multiplicity of electrode contacts on the electrode array, said alterphasic inverting stimulation comprises a multiplicity of cycles on a multiplicity of channels, wherein at least one cycle of the multiplicity of cycles includes alterphasic inverting monophasic pulses occurring within the multiplicity of channels; and
- modulating the stimulation pulses provided by the alterphasic inverting stimulation with sound information.
10. A method of providing a low power stimulation strategy for use within a cochlear stimulation system, said stimulation system including an electrode array insertable into a human cochlea, wherein the electrode array has a multiplicity of spaced-apart electrode contacts positioned at or near its distal end, the method comprising:
- applying an alterphasic inverting stimulation to at least a multiplicity of the multiplicity of electrode contacts on the electrode array; and
- modulating the stimulation pulses provided by the alterphasic inverting stimulation with sound information;
- wherein applying the alterphasic inverting stimulation comprises: stimulating a first electrode contact on the electrode array with a monophasic pulse having a first polarity; stimulating a second electrode contact on the electrode array following stimulation of the first electrode contact with a monophasic pulse having a second polarity, wherein the second polarity is the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially near the first electrode contact, and wherein the second polarity is the same polarity or the opposite polarity of the pulse applied to the first electrode contact whenever the second electrode contact is spatially far from the first electrode contact; stimulating a third electrode contact on the electrode array following stimulation of the second electrode contact with a monophasic pulse having a third polarity, wherein the third polarity is the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially near the second electrode contact, and wherein the third polarity is the same polarity or the opposite polarity of the pulse applied to the second electrode contact whenever the third electrode contact is spatially far from the second electrode contact; continuing to stimulate electrode contacts on the electrode array following the above pattern until a desired number of electrode contacts have been stimulated; and repeating the above stimulation pattern for all of the electrode contacts on the electrode array that are stimulated by a first monophasic pulse of one polarity by stimulating that electrode contact with a second monophasic pulse of an opposite polarity, whereby a selected number of the electrode contacts on the electrode array are stimulated sequentially in accordance with the alterphasic inverting stimulation strategy.
11. The stimulation strategy of claim 6 wherein the at least one cycle includes a time gap of T1 seconds between two monophasic pulses, wherein T1 ranges from 1 to 100 μs.
12. The method of claim 9 further including inserting a time gap of T1 seconds between two monophasic pulses for the at least one cycle, wherein T1 ranges from 1 to 100 μs.
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Type: Grant
Filed: Nov 19, 2004
Date of Patent: Jan 23, 2007
Assignee: Advanced Bionics Corporation (Valencia, CA)
Inventors: Stefaan Peeters (Aartselaar), Filiep Vanpoucke (Huldenberg)
Primary Examiner: Robert Pezzuto
Assistant Examiner: Shevon Johnson
Attorney: Bryant R. Gold
Application Number: 10/993,991
International Classification: A61N 1/32 (20060101);